Optical bench on substrate and method of making the same

ABSTRACT

An optical bench including a substrate having a trench with the trench having an angled sidewall on which a reflective coating is provided. The optical bench also includes a first device and a waveguide positioned within the trench, a second device optically connected to the first device, and at least one active circuit electrically connected to the first device with the waveguide being positioned optically between the first device and the reflective coating. The optical bench also includes an optically transparent material that forms a first interface with the first device and a second interface with a first surface of the waveguide.

PRIORITY CLAIM

The present application is a continuation of U.S. application Ser. No. 14/699,151, filed Apr. 29, 2015, which was a continuation-in-part of U.S. application Ser. No. 13/403,566, filed Feb. 23, 2012, both of which are incorporated herein by reference in their entireties.

TECHNICAL FIELD

The present disclosure relates generally to an integrated circuit.

BACKGROUND

A multi-chip module package (MCM) integrates chips with different functions and made of different processes. Some MCMs utilize substrate materials based on ceramic or organic polymers, which, in certain configurations, may have insufficient coefficient of thermal expansion (CTE) matching to semiconductor chips and/or heat dissipation property. This causes potential reliability issues for III-V semiconductor material based optoelectronic chips and/or high power amplifiers.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a cross-sectional diagram of an optical bench on substrate according to some embodiments;

FIGS. 2A-2E are cross-sectional diagrams of various steps of fabrication process of the optical bench on substrate in FIG. 1 according to some embodiments;

FIGS. 3A-3C are cross-sectional diagrams of various steps of another fabrication process of the optical bench on substrate in FIG. 1 according to some embodiments; and

FIG. 4 is a cross-sectional diagram of an optical bench on a substrate according to some embodiments.

DETAILED DESCRIPTION

The making and using of various embodiments are discussed in detail below. It should be appreciated, however, that the present disclosure provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use, and do not limit the scope of the disclosure.

In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. Moreover, the formation of a feature on, connected to, and/or coupled to another feature in the present disclosure that follows may include embodiments in which the features are formed in direct contact, and may also include embodiments in which additional features may be formed interposing the features, such that the features may not be in direct contact. In addition, spatially relative terms, for example, “lower,” “upper,” “horizontal,” “vertical,” “above,” “below,” “up,” “down,” “top,” “bottom,” etc. as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) are used for ease of the present disclosure of one features relationship to another feature. The spatially relative terms are intended to cover different orientations of the device including the features.

FIG. 1 is a schematic diagram of an optical bench 100 on substrate according to some embodiments. The optical bench 100 includes a laser diode land a photo diode 2 mounted on a substrate 3. The laser diode 1 and the photo diode 2 comprise III-V semiconductor materials and operate on electromagnetic wavelengths in the range of 450 nm-1700 nm in some embodiments. The substrate 3 comprises any suitable material, such as silicon. An etching hard mask 4 comprises SiN or SiO₂ and is able to achieve at least 30 μm etch depth in some embodiments. The etching hard mask layer 4 over the area for a trench 21 and/or an optical waveguide 19 is removed. In some examples, the etching hard mask layer 4 comprises SiN of at least 30 nm in thickness. In further examples, the etching hard mask layer 4 comprises SiO₂ of at least 100 nm in thickness. A reflector layer 5 comprises at least one of Cu, Al, Ag, or Au, multi-layered dielectrics, or any other suitable material having a reflective property at desired electromagnetic wavelengths. In some embodiments, the reflector layer 5 has at least 90% reflectivity at selected wavelengths. In some embodiments, a material of reflector layer 5 is chosen to selectively reflect a desired waveband and to either absorb or transmit wavelengths outside the desired waveband.

A dielectric layer 6 comprises SiO₂ or other low-k dielectric materials such as porous SiO₂, organic polymers such as polymide or Polybenzobisoxazole (PBO), or hybrid-organic polymers such as polysiloxane in some embodiments. To achieve high performance at radio frequency (RF) and microwave frequency, the thickness of the dielectric layer 6 is at least 300 nm where substrate 3 is a high resistance silicon substrate (resistivity >3000 ohm-cm) in some embodiments. The thickness of the dielectric layer 6 is at least 1 μm where substrate 3 is part of normal resistance wafers (resistivity is from 1 ohm-cm to 10 ohm-cm) in some embodiments.

A redistribution layer (RDL) 7 over the substrate 3 is an electrically conductive layer on a chip that allows the Input Output (TO) pads of an integrated circuit available in other locations. The RDL 7 comprises Al, Cu, or any other suitable electrically conductive material, and has more than 1 μm thickness for high speed applications over 2 Gbps in some embodiments. A passivation layer 8 comprises SiO₂, SiON, SiN, multi-stacks of these materials, or any other suitable materials in some embodiments. The thickness of the passivation layer 8 is from about 200 nm to about 800 nm for pad protection in some embodiments.

A bottom cladding layer 9 comprises SiO₂/SiON in some embodiments. Bottom cladding layer 9 is formed by plasma-enhanced chemical vapor deposition (PECVD) in some embodiments. In some embodiments, spin-on dielectrics or polymers are used to form the bottom cladding layer 9. The thickness of the bottom cladding layer 9 is at least 500 nm in some embodiments to prevent optical leakage. A core layer 10 comprises SiON/SiN in some embodiments. Core layer 10 is formed by plasma-enhanced chemical vapor deposition (PECVD) in some embodiments. In some embodiments, spin-on dielectrics or polymers are used to form the core layer 10. The thickness of the core layer 10 is at least 15 μm in some embodiments. A top cladding layer 11 comprises SiO₂/SiON in some embodiments. Top cladding layer 11 is formed by plasma-enhanced chemical vapor deposition (PECVD) in some embodiments. In some embodiments, spin-on dielectrics or polymers are used to form the top cladding layer 11. The thickness of the top cladding layer 11 is at least 500 nm in some embodiments to prevent optical leak. In some embodiment, an optical fiber can be placed in the trench 21 as the waveguide 19.

The bottom cladding layer 9, the core layer 10, and the top cladding layers 11 form the waveguide 19 inside a trench 21 as an optical link medium for the electromagnetic wavelengths used by the laser diode 1 and/or the photo diode 2. The refractive index of the core layer 10 is higher than that of the bottom and top cladding layers 9 and 11, and the refractive index difference is at least 0.02 in some embodiments to prevent optical leakage. In at least one example, three polymer layers for the bottom cladding layer 9, the core layer 10, and the top cladding layer 11 are deposited by a spin on process, and then a lithography process is used to define dimensions of the optical waveguide 19. An optical path 20 is an exemplary light path of light (electromagnetic wave) emitted from the laser diode 1, reflected by first a sloping side of the reflector layer 5, through the optical waveguide 19, reflected by a second sloping side of the reflector layer 5, then to the photo diode 2.

An under-bump metallization (UBM) layer 12 comprises any suitable under-bump metallurgy, e.g., Cu/Ni, in some embodiments. A bump layer 13 comprises lead-free solder or gold bumps in some embodiments. In some embodiments, bump layer 13 comprises a copper pillar. The bump layer 13 comprises micro bumps for flip-chip bonding with semiconductor-based optical and electrical chip in some embodiments. The overall thickness for the UBM layer 12 and the bump layer 13 is from about 1 μm to about 15 μm in some embodiments. Through substrate vias (TSVs) 14 formed through the substrate 3 comprises Cu or any other suitable electrically conductive materials in some embodiments. The TSVs 14 are used to provide backside electrical connections, and are fabricated using any suitable methods and materials known in the art.

Another dielectric layer 15 comprises SiO₂ or other low-k dielectric material such as porous SiO2, organic polymers such as polymide or Polybenzobisoxazole (PBO), or hybrid-organic polymers such as polysiloxane in some embodiments. To achieve high performance at radio frequency (RF) and microwave frequency, a thickness of the dielectric layer 15 is at least 300 nm where substrate 3 is a high resistance silicon substrate (resistivity >3000 ohm-cm) in some embodiments. The thickness of dielectric layer 15 is at least 1 μm where substrate 3 is part of normal resistance wafers (resistivity is from 1 ohm-cm to 10 ohm-cm) in some embodiments. A backside redistribution layer (RDL) 16 comprises Al, Cu, or any other suitable electrically conductive material, and has more than 1 μm thickness for high speed applications over 2 Gbps in some embodiments.

The trench 21 has sloping sides with a slope angle θ ranging from about 42° to about 48° with respect to a top surface of substrate 3 and has a depth of more than 30 μm in some embodiments to accommodate the optical beam from the laser diode 1, e.g., a vertical cavity surface emitting laser (VCSEL). In some embodiments, laser diode 1 has a beam diversion angle of about 20°-30° with a beam size of about 10 μm to about 15 μm.

The integrated optical bench 100 on substrate facilitates coupling the light from the laser diode 1 to the reflector layer 5 and into the waveguide 19. The integrated optical ben 100 also leads the light out of waveguide 19 to the reflector layer 5 to be received by the detector diode 2. The optical bench 100 on substrate is implemented with one portion on either side of the line 22 in some embodiments. For example, in one or more embodiments, the optical bench 100 includes the transmitting portion on the left side of the line 22 and having the laser diode 1 as a transmitter. In one or more embodiments, the optical bench 100 includes the receiving portion on the right side of the line 22 and having the photo diode 2 as a receiver. The large waveguide 19 dimension (greater than 15 μm in some embodiments) also allows light to be coupled into and out of optical fibers for out-of-chip communication with separate chips of a semiconductor device.

The optical bench 100 on substrate structure can provide better coefficient of thermal expansion (CTE) matching and/or heat dissipation for optical components such as the laser diode 1 and the photo diode 2 mounted on the substrate 3 when the substrate 3 comprises semiconductor materials such as silicon, compared to other substrate or interposer materials such as ceramic or organic polymer. More robust and cost efficient integration of optics using silicon micro-fabrication technology is achieved by the optical bench 100 on substrate compared to some other assembly using discrete optical components. Also, there is less crosstalk among optical channels by using the optical waveguide 19 to help secure data transfer.

Furthermore, by configuring the optical bench 100 as a transmitting portion (e.g., the portion on the left side of the line 22 and having the laser diode 1 as a transmitter), or as a receiving portion (e.g., the portion on the right side of the line 22 and having the photo diode 2 as a receiver), inclusion of an optical input/output off the package is possible. This optical bench 100 on substrate platform offers higher data rate transfers inside the package than typical electrical connections by integrating optical components and optical options for signal input and output.

FIGS. 2A-2E are schematic diagrams of various steps of fabrication process of the optical bench on substrate in FIG. 1 according to some embodiments. In FIG. 2A, the RDL 7 is formed over the dielectric layer 6, e.g., by physical vapor deposition (PVD), for metal routing and metal traces for high speed electrical signal propagation. The passivation layer 8 (e.g., silicon nitride or oxide) is deposited afterward for metal protection, e.g., by chemical vapor deposition (CVD). The passivation layer 8, the dielectric layer 6, and the etching hard mask 4, e.g., silicon nitride or silicon oxide, are removed from an area where the trench 21 is to be formed.

In FIG. 2B, the trench 21 (at least 30 μm deep in some embodiments), including the sloping sides with a slope angle θ, is fabricated by wet etching using KOH(aq)/IPA or TMAH solution. One method to control the anisotropic wet etching is achieved by using KOH (25 wt %-35 wt %) with no less than 5 wt % IPA quantity. The temperature is kept at about 60° C.-70° C. during the wet etching to achieve a reasonable etch rate of 0.2-0.6 microns per minute during the wet etching and to prevent excessive hillock formation.

The reflector layer 5 having sloping sides with a slope angle θ (e.g., 42°-48°) is formed on the trench 21. This step may include depositing an adhesion dielectric layer, then a barrier/adhesion metal layer, such as Ti or Cr, and finally a highly reflective metal such as Al, Cu, Ag, or Au with a thickness greater than 50 nm to achieve reflectivity greater than 90% in some embodiments. The deposition process is performed by physical vapor deposition (PVD) or electroplating, in at least one example. Any other suitable reflective material or process is also usable.

In FIG. 2C, the waveguide 19, e.g., polymer, for the optical path inside the trench 21 is formed. This step includes forming the bottom cladding layer 9 (e.g., dielectric or polymer) by chemical vapor deposition (CVD) or a coater (for dielectric or polymer), then the core layer 10 (e.g., polymer), and the top-cladding layer 11 (e.g., dielectric or polymer) in some embodiments. The waveguide 19 can be defined by etching and unnecessary portions of the reflector layer 5 are removed in some embodiments. In some embodiments, a portion of an optical fiber is placed in the trench 21 as the waveguide 19.

In FIG. 2D, the UBM layer 12 such as Cu/Ni is formed, e.g., by evaporation or sputtering, or by chemically plating. A bump layer 13 is formed or placed on the UBM layer 12 in many ways, including evaporation, electroplating, printing, jetting, stud bumping, and direct placement.

In FIG. 2E, the laser diode 1 and the photo diode 2, as well as other driver or transimpedance amplifier (TIA) chips, are flip-chip mounted (and/or wire-bonded as necessary) over the substrate 3. In FIG. 2E, the portion on the left side of the line 22 is the transmitting portion of the optical bench shown in FIGS. 2A-2D, and the portion on the right side of the line 22 is a receiving portion that can be fabricated in the same or similar process flow described with respect to FIGS. 2A-2D.

FIGS. 3A-3C are schematic diagrams of various steps of another fabrication process of the optical bench on substrate in FIG. 1 according to some embodiments. In FIG. 3A, the etching hard mask 4 and the dielectric layer 6 are formed over the substrate 3. The etching hard mask 4, e.g., silicon nitride or silicon oxide, and the dielectric layer 6 are removed from an area where the trench 21 is to be formed.

In FIG. 3B, the trench 21 with the slope angle θ (as shown in FIG. 1) is formed by etching, e.g., using KOH(aq)/IPA or TMAH solution. One method to control the anisotropic wet etching is achieved by using KOH (25 wt %-35 wt %) with no less than 5 wt % IPA quantity. The temperature is kept at about 60° C.-70° C. during the wet etching to achieve a reasonable etch rate of 0.2-0.6 microns per minute during the wet etching and to prevent excessive hillock formation.

The reflector layer 5 having a slope angle θ (e.g., 42°-48°) is formed on the sloping side of the trench 21. This step may include depositing an adhesion dielectric layer, then a barrier/adhesion metal layer, such as Ti or Cr, and finally a highly reflective metal such as Al, Cu, Ag, or Au with a thickness greater than 50 nm to achieve reflectivity greater than 90% in some embodiments. The deposition process is performed by physical vapor deposition (PVD) or electroplating, in at least one example. Any other suitable reflective material or process is usable. The reflector layer 5 is removed in areas where it is not necessary by a lithography process in some embodiments.

In FIG. 3C, the RDL 7 is formed and defined for metal routing and metal traces for high speed electrical signal propagation. Additional dielectric layer for electrical isolation and microwave confinement can be formed as necessary. After the step in FIG. 3C, the process flow can proceed to the operation of forming the passivation layer 8 (e.g., silicon nitride or oxide) for metal protection as described with respect to FIG. 2A, and then proceed to the steps described in FIGS. 2C-2E afterwards.

FIG. 4 is a cross-sectional diagram of an optical bench 400 on a substrate according to some embodiments. Optical bench 400 includes similar elements as optical bench 100. Same elements have a same reference number. In comparison with optical bench 100, optical bench 400 includes laser diode 1 within trench 21. In some embodiments, laser diode 1 is called a light emitting device. RDL 7 electrically connects laser diode 1 to an active circuit 410. Active circuit 410 is configured to generate a signal to provide information to laser diode 1 for emitting light to be received by photodetector 2. In some embodiments, photodetector 2 is called a light receiving device. Optical bench 400 also includes an underfill material 420 between active circuit 410 and passivation layer 8 to help increase mechanical strength of optical bench 400 in comparison to structures which do not include underfill material 420. An optically transparent material 430 is between laser diode 1 and waveguide 19.

Optically transparent material 430 helps to increase an amount of light propagated between laser diode 1 and photodetector 2 by reducing light scattering, and reflection at an interface of laser diode 1 and a surrounding environment. Optically transparent material 430 increases an amount of light propagated between laser diode 1 and photodetector 2 due to refractive index matching. That is, a difference in a refractive index at an output of laser diode 1 and optically transparent material 430 is less than a difference in the refractive index at the output of the laser diode and the surrounding environment. In some embodiments, optically transparent material 430 comprises spin-on glass, an organic material, a polymer material, or another suitable material.

Trench 21 includes two sloped sides. In some embodiments, a side between active circuit 410 and laser diode 1 is substantially perpendicular to a top surface of substrate 3. In some embodiments, reflector layer 5 extends between a bottom surface of waveguide 19 and substrate 3. In some embodiments, reflector layer 5 is located only on the sloped side of trench 21.

Optical bench 400 includes a single active circuit 410 connected to laser diode 1. In some embodiments, optical bench 400 includes multiple active circuits 410 connected to laser diode 1. In some embodiments having multiple active circuits 410, laser diode is selectively connected to each of the active circuits 410. In some embodiments, a control system is configured to control which of the multiple active circuits 410 are connected to laser diode 1 at any particular time. In some embodiments, at least one active circuit 410 is selectively connected to laser diode 1 by a TSV, such as TSV 14.

Optical bench 400 includes laser diode 1 in trench 21. In some embodiments, photodetector 2 is located in trench 21 and laser diode 1 is located outside of the trench. In some embodiments, photodetector 2 is electrically connected to one or more active circuits similar to active circuit 410. Photodetector 2 is configured to convert a received optical signal from laser diode 1 into an electrical signal. This electrical signal is then provided to the at least one active circuit connected to photodetector 2. In some embodiments where multiple active circuits are connected to photodetector 2, a control system is configured to selectively determine which of the active circuits are connected to the photodetector at any one time. In some embodiments, the control system for controlling connections between active circuits 410 and laser diode 1 is a same control system as that for controlling connections between active circuits and photodetector 2. In some embodiments, the control system for controlling connections between active circuits 410 and laser diode 1 is different from the control system for controlling connections between active circuits and photodetector 2.

In some embodiments, both laser diode 1 and photodetector 2 are located within trench 21. In embodiments where both laser diode 1 and photodetector 2 are located within trench 21, waveguide 19 and optically transparent material 430 are between the laser diode and the photodetector. In some embodiments where both laser diode 1 and photodetector 2 are located within trench 21, the trench has no sloped sides or reflector layer 5 is omitted.

In some embodiments, optical bench 400 is formed in a manner similar to that described in FIGS. 2A-2E or in FIGS. 3A-3C. In comparison with the method of making described in FIGS. 2A-2E and FIGS. 3A-3C, optical bench 400 includes bonding laser diode 1 in trench 21 sequentially with forming waveguide 19. In some embodiments, waveguide 19 is formed in trench 21 prior to bonding of laser diode 1 in trench 21. In some embodiments, waveguide 19 is formed in trench after bonding of laser diode 1 in trench. In some embodiments, at least a part of waveguide 19 is formed in trench 21 simultaneously with boding laser diode 1 in trench 21. Following bonding laser diode 1 and waveguide 19 in trench 21, optically transparent material 430 is deposited around waveguide 19. In some embodiments, optically transparent material 430 is deposited using a spin-on process, a PVD process or a CVD process. In some embodiments, a material removal step, such as etching, is used to remove optically transparent material 430 from undesired locations following the deposition step. In some embodiments where photodetector 2 is in trench 21, the photodetector is bonded in the trench sequentially with formation of waveguide 19 in the trench. In some embodiments where photodetector 2 is in trench 21, the photodetector is bonded in the trench simultaneously with formation of at least a part of waveguide 19 in the trench. In some embodiments where both photodetector 2 and laser diode 1 are in trench 21, the photodetector is bonded in the trench sequentially with the laser diode. In some embodiments where both photodetector 2 and laser diode 1 are in trench 21, the photodetector is bonded in the trench simultaneously with the laser diode.

One aspect of this description relates to a first embodiment of an optical bench. The optical bench includes a substrate having a trench therein with a reflective coating formed on an angled sidewall of the trench. The optical bench also includes a first device positioned within the trench, a second device optically connected to the first device, at least one an active circuit electrically connected to the first device. In addition to the first device, the optical bench includes a waveguide in the trench with the waveguide being positioned optically between the first device and the reflective coating. The optical bench also includes an optically transparent material that forms a first interface with the first device and a second interface with a first surface of the waveguide.

Another aspect of this description relates to another embodiment of an optical bench. The optical bench has a substrate in which a trench is formed with a reflective coating provided over an angled sidewall of the trench. The optical bench also includes a light emitting device within the trench, a light receiving device optically connected to the light emitting device, and at least one active circuit electrically connected to the light emitting device. In addition to the light emitting device, the optical bench includes a waveguide positioned in the trench and positioned optically between the light emitting device and the reflective coating. The optical bench also includes an optically transparent material that forms a first interface with the light emitting device and a second interface with a first surface of the waveguide.

Still another aspect of this description relates to another embodiment of an optical bench. The optical bench includes a substrate that has a trench that includes a first angled sidewall having a first slope angle and a reflective coating on the angled sidewall. The optical bench also includes a light receiving device provided within the trench and a light emitting device optically connected to the light receiving device and electrically connected to a transmitting circuit. The optical bench also includes a waveguide provided in the trench and positioned optically between the light receiving device and the reflective coating. The optical bench also includes an optically transparent material that forms an interface with the light receiving device and an interface with a first surface of the waveguide.

It will be readily seen by one of ordinary skill in the art that the disclosed embodiments fulfill one or more of the advantages set forth above. After reading the foregoing specification, one of ordinary skill will be able to affect various changes, substitutions of equivalents and various other embodiments as broadly disclosed herein. Although features of various embodiments are expressed in certain combinations among the claims, it is contemplated that these features can be arranged in any combination and order. It is therefore intended that the protection granted hereon be limited only by the definition contained in the appended claims and equivalents thereof. 

What is claimed is:
 1. An optical bench comprising: a substrate having a trench therein; a reflective coating over an angled sidewall of the trench; a first device within the trench; a second device optically connected to the first device; at least one active circuit electrically connected to the first device; a waveguide in the trench, wherein the waveguide is optically between the first device and the reflective coating; and an optically transparent material, the optically transparent material forming a first interface with the first device and a second interface with a first surface of the waveguide.
 2. The optical bench according to claim 1, wherein: the optically transparent material forms a third interface with a second surface of the waveguide.
 3. The optical bench according to claim 2, wherein: the optically transparent material forms a fourth interface with a first surface of the reflective coating.
 4. The optical bench according to claim 1, wherein: the second device is above the angled sidewall of the trench.
 5. The optical bench according to claim 1, wherein: the waveguide comprises: a first cladding material having a first refractive index, and a core material having a second refractive index, wherein the second refractive index is at least 0.02 greater than the first refractive index.
 6. The optical bench according to claim 5, wherein: the waveguide further comprises a second cladding material having a third refractive index, wherein the second refractive index is at least 0.02 greater than the third refractive index.
 7. The optical bench according to claim 1, wherein: the waveguide comprises an optical fiber wherein a first cladding material having a first refractive index surrounds a core material having a second refractive index, and the second refractive index is at least 0.02 greater than the first refractive index.
 8. The optical bench according to claim 1, wherein: the angled sidewall of the trench has a slope angle θ of between about 42° and about 48°.
 9. The optical bench according to claim 1, wherein: the reflective coating comprises an adhesion layer over the angled sidewall, a barrier layer over the adhesion layer, and a reflective metal layer over the barrier layer.
 10. The optical bench according to claim 1, wherein: the reflective coating has a reflectivity of at least 90%.
 11. An optical bench comprising: a substrate having a trench therein; a reflective coating over an angled sidewall of the trench; a light emitting device within the trench; a light receiving device optically connected to the light emitting device; at least one active circuit electrically connected to the light emitting device; a waveguide in the trench, wherein the waveguide is optically between the light emitting device and the reflective coating; and an optically transparent material, the optically transparent material forming a first interface with the light emitting device and a second interface with a first surface of the waveguide.
 12. The optical bench according to claim 11, further comprising: a plurality of active circuits, each active circuit of the plurality of active circuits being electrically connectable to the light emitting device; and a control system for selectively connecting at least one of the active circuits to the light emitting device.
 13. The optical bench according to claim 11, wherein: the reflective coating extends under a first portion of the waveguide.
 14. The optical bench according to claim 11, wherein: the optically transparent material comprises a spin-on glass (SOG), an organic material, or a polymeric material.
 15. The optical bench according to claim 11, wherein: the light emitting device has a first refractive index at an output surface; the optically transparent material has second refractive index; and a surrounding environment has a third refractive index, wherein a difference between the first refractive index and the second refractive index is less than a difference between the first refractive index and the third refractive index.
 16. The optical bench according to claim 11, wherein: the at least one active circuit is electrically connected to the light emitting device by a through silicon via (TSV) structure.
 17. An optical bench comprising: a substrate having a trench therein; a reflective coating over a first angled sidewall of the trench, the first angled sidewall having a first slope angle; a light receiving device within the trench; a light emitting device optically connected to the light receiving device; at least one transmitting circuit electrically connected to the light transmitting device; a waveguide in the trench, wherein the waveguide is optically between the light receiving device and the reflective coating; and an optically transparent material, the optically transparent material forming a first interface with the light receiving device and a second interface with a first surface of the waveguide.
 18. The optical bench according to claim 17, further comprising: a second angled sidewall having a second slope angle, wherein the first slope angle is less than the second slope angle.
 19. The optical bench according to claim 17, further comprising: at least one receiving circuit electrically connected to the light receiving device.
 20. The optical bench according to claim 17, further comprising: a plurality of transmitting circuits, each of the transmitting circuits being electrically connectable to the light emitting device; a plurality of receiving circuits, each of the receiving circuits being electrically connectable to the light receiving device; and a control system configured for selectively connecting at least one of transmitting circuit of the plurality of transmitting circuits to the light emitting device and selectively connecting at least one receiving circuit of the plurality of receiving circuits to the light receiving device. 